Dengue, a vector-borne disease about which little was known prior to the 1990s, has now become endemic to the country, particularly the national capital region of Delhi. It breaks out with almost unfailing regularity during the monsoon season. Yet, hardly any attempt has been made to evolve a long-term strategy to combat it. This year's spread of dengue is by far the worst since 1996. Of over a dozen states that have been affected by it, Delhi alone has recorded over 3,800 confirmed cases and 19 deaths. States like Karnataka, Kerala, Tamil Nadu and Maharashtra are not far behind. The actual tally is bound to be higher as many cases go unreported and even unconfirmed since the facilities for conducting the reliable ELISA test are available only in a few government or private hospitals.
The reasons for the dengue menace getting out of control this year are many. For one, the civic authorities have been too slow to react to the emerging threat. Though the warning signals of the dengue outbreak were available as early as in July, anti-larval operations were initiated only when people actually began to die. Besides, co-circulation of more than one strains of the dengue virus has worsened the situation. Normally, only one or two serotypes, usually Type-I and Type-III, of the four serotypes of dengue virus are noticed in a season. When the dominant strains remain unchanged over a period, a significant section of the population tends to develop immunity to them. But this time, all the four types of virus, including the relatively more virulent Type-II and Type-IV, have become active. These virus strains cause haemorrhagic fever with a severe drop in platelets that can lead to organ failure and death. The worrying development is that Type-IV has been noticed almost for the first time. Not much scientific work has gone into finding the control of these viruses.
Moreover, ever since a ban has been enforced on cheap and highly effective pesticides like endosulfan and dichlorodiphenyltrichloroethane or DDT, the mosquito-control programmes have suffered as their alternatives are too costly for the fund-starved civic bodies to use and stay within their budgets. This has contributed to the surge in the incidence of dengue and other vector-borne infections, such as malaria, chikungunya and encephalitis in different parts of the country. The health care budgets of the Centre and states, therefore, need to be stepped up significantly to stave off such disease epidemics.
This aside, in the absence of any commercially available vaccine for dengue, its prevention by controlling mosquitoes and limiting exposures to bites is the only way to keep this dreaded disease under check. Unfortunately, stereotype approaches like pesticide sprays and fogging are still the main instruments for combating vector-borne diseases. These operations fail to produce satisfactory results unless undertaken regularly. Several new and unconventional approaches have been tried out with a fair degree of success in some other countries. Mexico, Venezuela and some African countries, for instance, have found good results with insecticide-treated curtains and mosquito nets. Vietnam has effectively used biological methods to control larvae in water bodies, including household tanks. Indonesia has experimented with devices to trap insect eggs to prevent pest multiplication. It is time India learnt from their experiences and adapted some of their methods to local conditions to keep dengue-like health contingencies at bay.
